LED lamp applications, including those comprising high-powered LEDs, are being developed at an increasing rate. LEDs, unlike more conventional light sources such as tungsten, halogen or HID light sources, emit essentially no infrared radiation and are, therefore, “cold” on their optical output side. Nevertheless, LEDs do generate heat at their electrical junction, the so-called “back side,” of the LED proper. This is particularly significant as the drive current increases in order to achieve greater LED optical output. Control of this thermal output, referred to as “junction temperature,” is critical so as to ensure proper operating performance of the LED and avoid either premature degradation or failure.
With the “back side” of the LEDs being housed within the lamp housing, which housing is conventionally made primarily of plastic, the heat generated is “trapped” within the housing. This thermal output on the “back side” of LEDs must be removed in order to prevent overheating and, relatedly, premature failure of the LED lamp. Accordingly, LEDs do require cooling via the introduction of heat sinks.
Conventionally, it is the practice to place such heat sinks within the housing of the LED lamp, where the LEDs themselves are housed. For instance, the head and tail-lamps for the CADILLAC CTS brand automobile utilize a single, high-power LED and a die-cast heat sink that dissipates heat within the housing of the lamp. Given that there is, for these particular applications, a sufficient amount of interior volume in which to dissipate this energy, such heat sinks serve their purpose. However, either for smaller volumes or applications generating additional thermal input, adequate dissipation of heat internally is complicated, thereby forcing the adoption of more elaborate thermal management solutions, such as exposing the heat sink to the outside of the housing or utilizing “heat pipes” (liquid filled thermal conductors) or cooling fans to circulate air within the lamp housing.
Still another solution, disclosed in United States Patent Application Pub. No. US 2007/0127252 A1 to Fallahi et al., published Jun. 7, 2007, comprises an LED headlamp assembly for a motor vehicle having a plastic lens and a plastic lamp housing cooperating with the lens to define an inner chamber that is generally fluidly isolated from the atmosphere. A cast metal reflector is mounted to the lamp housing and has a polished reflective portion that reflects light forward through the lens. A separate heat sink portion of the reflector includes fins that extend through the lamp housing and are exposed to the atmosphere outside the lamp housing, such that heat from the inner chamber is transmitted from the fins to the atmosphere.
The foregoing thermal management solutions notwithstanding, it is desirable to have a lamp assembly, for automotive as well as other applications, that is able to effectively dissipate heat energy generated by LEDs or other light sources.